Low-friction reciprocating pump

ABSTRACT

A reciprocating pump for pumping a fluid, especially for pumping a fluid such as UV ink which is subject to solidification when exposed to frictional forces. The pump has an internal displacement chamber with an inlet, and outlet, and a plunger which is reciprocally movable in the chamber. The plunger reciprocates through an axial passage in the housing at one end of the chamber, the passage being sized to receive the plunger with a clearance fit. First and second seals are positioned in the axial passage. Each seal is annular in shape and extends between the plunger and housing in sealing contact therewith. The pump housing is free from a bearing which contacts the plunger or guides its motion, such that the sealing contacts between the plunger and seals are the only contacts of the plunger in the housing.

BACKGROUND OF THE INVENTION

This invention relates to reciprocating pumps for pumping fluids, andmore particularly to a pump which lengthens the operational life of thepump by reducing the frictional forces expended on the fluid beingpumped. The pump is described primarily herein for application inpumping a fluid which is subject to solidification when exposed tofrictional forces. However, it is understood that the pump and sealassembly may be applied to efficiently pump any type of fluid.

Ink that is cured with ultraviolet (UV) energy has widespread use in theprinting and graphic display industries. That type of ink is highlyviscous and has a unique chemistry which requires special handling andpumping needs. Its material composition includes a monomer, instead of asolvent as in conventional inks, such that it solidifies whenirradiated. Unfortunately, UV ink is also sensitive to mechanical shearstress (i.e., friction) which produces heat and initiates solidificationof the ink. Conventional displacement pumps expose UV ink to substantialfriction as it is pumped. Consequently, solidified polymers form andaccumulate in the pump which cause the pump to bind and ultimately fail.Of particular concern are gaps between close-fitting parts which haverelative movement. For example, a conventional pump has a reciprocalplunger received in a stationary bearing or sleeve for guiding movementand preventing “wobble” of the plunger as it reciprocates. The close-fitsliding motion produces localized regions of high friction at small gapsbetween the plunger and the bearing or sleeve. UV ink which reachesthese gaps is prone to solidify. Aggravating this problem is that theplunger assembly must be sealed to prevent leaks.

SUMMARY OF THE INVENTION

Among the several objects and features of the present invention may benoted the provision of a fluid pump which exerts less frictional forceon the fluid being pumped; the provision of such a pump whicheffectively pumps a highly viscous fluid including UV ink; the provisionof such a pump which is sealed to prevent leakage of fluid; and theprovision of such a pump which is efficient and durable in use andcost-efficient to construct.

In general, a reciprocating pump of the present invention is for pumpinga fluid. The pump comprises a pump housing having an internaldisplacement chamber with an inlet, and outlet, a longitudinal axis, andopposite ends. A plunger is reciprocally movable in the chamber alongthe axis. An axial passage is in the housing at one end of the chamberthrough which the plunger axially reciprocates. First and second annularseals in the axial passage are generally co-axial with the passage andspaced from one another longitudinally of the passage. Each seal issized for sealing contact with the plunger. The pump housing is freefrom a bearing which contacts the plunger or guides its motion. Theplunger is free from direct engagement with the housing, and the sealingcontacts of the plunger with the first and second seals are the onlycontacts of the plunger in the housing.

In another aspect, a reciprocating pump of this invention is for pumpinga fluid. The pump includes a pump housing having an internaldisplacement chamber with an inlet, and outlet, a longitudinal axis, andopposite ends. A plunger is reciprocally movable in the chamber alongthe axis. An axial passage is in the housing at one end of the chamberthrough which the plunger axially reciprocates, the axial passage havingat least a portion which defines a minimum clearance region for theplunger in the housing. The minimum clearance region is sized to receivethe plunger therethrough with a clearance fit. The plunger has an outerdiameter D1, the minimum clearance region has an internal diameter D2,and D2 is larger than D1 by at least about 0.015 inch.

In yet a further aspect, a reciprocating pump of this invention is forpumping a fluid. The pump comprises a pump housing having an internaldisplacement chamber with an inlet, and outlet, a longitudinal axis, andopposite ends. A plunger is reciprocally movable in the chamber alongthe axis. An axial passage is in the housing at one end of the chamberthrough which the plunger axially reciprocates, the axial passage havingat least a portion which defines a minimum clearance region for theplunger in the housing. The minimum clearance region of the axialpassage has an axial length L1 which is less than 1.0 inch.

In still another aspect, a reciprocating pump according to the presentinvention is for pumping a fluid. The pump comprises a pump housinghaving an internal displacement chamber with an inlet, and outlet, alongitudinal axis, and opposite ends. The housing includes a pump head,a cylinder attached to the head, and a gland attached to the headgenerally opposite the cylinder. A plunger is reciprocally movable inthe chamber along the axis. An axial passage is in the gland throughwhich the plunger axially reciprocates. First and second annular sealsin the axial passage are generally co-axial with the passage and spacedfrom one another longitudinally of the passage. Each seal is sized forsealing contact with the plunger and has a generally U-shapedcross-section with two opposing legs in respective sealing contact withthe plunger and housing. The two legs of each seal are asymmetrical. Theaxial passage comprises an intermediate section between the seals whichis sized to receive the plunger therethrough with a clearance fit.Internal shoulders are at opposite longitudinal ends of the intermediatesection. Each of the seals is positioned adjacent a respective shoulderin the axial passage, at least one of the seals being retained by athreaded nut. The pump housing is free from a bearing which contacts theplunger or guides its motion. The plunger is free from direct engagementwith the housing, and the sealing contacts of the plunger with the firstand second seals are the only contacts of the plunger in the housing.

Other objects and features of the present invention will be in partapparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a system for pumping fluid with a pump of thisinvention;

FIG. 2 is a perspective of the pump;

FIG. 3 is a vertical section of the pump;

FIG. 4 is an enlarged fragment of FIG. 3;

FIG. 5 is a vertical section of a gland of the pump; and

FIG. 6 is a perspective of the gland.

Corresponding reference characters indicate corresponding partsthroughout the views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and in particular to FIG. 1, a pumpaccording to the present invention for delivering fluid to a devicerequiring fluid is indicated generally at 10. The pump 10 may be used,for example, in pumping ink from a supply container 12 (e.g., a drum) tofountains of a printing press 14. In one embodiment, the pump 10 issupported upon a follower plate 16 near the upper surface of fluid inthe container 12. The plate 16 and pump 10 move downward in thecontainer 12 as fluid is removed and the elevation of the upper surfaceof fluid is lowered. The pump 10 has a cylinder 20 which, in oneembodiment, is oriented vertically with its lower end submerged in fluidof the container 12. The lower end of the cylinder has an openingcomprising an inlet 22 for receiving fluid. A motor 24 is positionedabove the pump for driving the pump, and a transverse outlet tube 26extends away from the pump for delivery of fluid to the printing press14. It is understood that the pump 10 can have other arrangements ororientations without departing from the scope of this invention.

As shown in FIG. 2, the pump 10 comprises a housing, indicated generallyat 30, including a head 32 which is generally cylindric in shape and hasa mounting flange 34. The cylinder 20 extends from the head 32 inlongitudinal alignment with the head. The flange 34 has bores 36 forreceiving tie rods (not shown) to fasten the head 32 to the motor 24. Aconnector 38 and coupling nut 39 are provided for operative connectionof the pump 10 to a powered drive shaft (not shown) of the motor 24. Anoutlet 40 extends from the head 32 for connection to the outlet tube 26.

Referring to FIG. 3, the head 32 and cylinder 20 define an internaldisplacement chamber, indicated generally at 42, with a longitudinalaxis C. A plunger 44 is reciprocally movable in the chamber 42 along theaxis. In one embodiment, the plunger 44 is cylindric, having an outer(radial) diameter D1. In one embodiment, the external surface of theplunger 44 includes a material which is smooth and inhibits frictionwith fluid as it moves therepast. An exemplary surface material is aseries of nickel-based alloy coatings deposited according to MAGNAPLATEHMF®, a process which is proprietary to the General MagnaplateCorporation having offices in Linden, N.J. The pump 10 has a first checkvalve 46 at the inlet 22 for permitting one-directional flow of fluidinto the chamber 42. A second check valve 48 at the outlet 40 allowsone-directional flow of fluid out from the chamber 42. In oneembodiment, the first and second check valves 46, 48 have conventionalround balls and corresponding seats. That type of valve closes quicklyand reduces the possibility of small openings or gaps which would exposethe fluid to shear stress as it passes through a partially closed valve.

The pump 10 is known to those skilled in the art as a “single-acting”type pump having a pumping cycle which discharges fluid only during astroke of the plunger 44 in one direction. During an upstroke, theplunger 44 moves outward (up in FIG. 3), the first check valve 46 isopen, and fluid is drawn through the inlet 22 into the chamber 42. Thesecond check valve 48 is closed and blocks any discharge. During adownstroke, the plunger 44 moves inward, the first check valve 46 isclosed, and the plunger displaces fluid in the chamber 42 such that itopens the second valve 48. Fluid is then discharged through the outlet40 while the first check valve 46 remains closed. Other configurationsof the pump 10 do not depart from the scope of this invention. Inparticular, it is understood that the pump could be a “double-acting”pump wherein fluid is forced between two separate chambers in the pump,and fluid is discharged during a pumping cycle on both an upstroke and adownstroke.

The pump housing 30 includes a gland 50 secured (e.g., threaded) in thehead 32 generally opposite the cylinder 20. The gland 50 defines anaxial passage, indicated generally at 52, at one end (e.g., the upperend) of the chamber 42 through which the plunger 44 axiallyreciprocates. The gland 50 is shown in isolated detail in FIGS. 5 and 6.The gland has a generally cylindric external surface which includesscrew threads 54 on an upper portion thereof. The upper portion isformed with a hexagonal gripping flange 56. An annular groove 58 extendsaround a lower portion of the external surface of the gland 50 forreceiving an O-ring seal 60, shown in FIG. 4, to prevent leaks betweenthe gland and head 32.

In the embodiment shown in FIG. 5, the axial passage 52 comprises anouter (upper) section 62 defined by a first generally cylindric surface,an intermediate section 64 inward of (below) the outer section definedby a second generally cylindric surface, and an inner (lower) section 66defined by a third generally cylindric surface. As shown, theintermediate section 64 has an internal diameter D2; the upper section62 has an internal diameter D3 greater than D2; and the lower section 66has an internal diameter D4 greater than D2, with D3 and D4 beingapproximately the same in the illustrated embodiment. As shown in FIG. 5and discussed more fully below, the intermediate section 64 of the axialpassage 52 has an axial length designated L1, and the upper and lowersections 62, 66 have axial lengths designated L2 and L3, respectively.Due to the relative sizing of the internal diameters of the upper,intermediate and lower sections of the passage, the plunger 44 asreceived in the gland 50 is spaced relatively closer in a radialdirection to the generally cylindric surface of the intermediate section64 than to the surfaces of the upper and lower sections 62, 66. Thechanges in the internal diameter of the axial passage 52 form an outer(upper) flat annular shoulder 68 at the juncture of the upper andintermediate sections 62, 64 of the axial passage. Similarly, an inner(lower) flat annular shoulder 70 is formed at the juncture of the lowerand intermediate sections 66, 64 of the axial passage. It is understoodthat the gland 50 may have continuous, gradual changes in diameter, adifferent arrangement of sections, a fewer or greater number of sections(including only one section of uniform diameter), and/or may beintegrally formed with the head without departing from the scope of thisinvention.

An annular groove 72 extends around the intermediate section 64 of theaxial passage 52 and communicates with a transverse drain bore 74 fordraining fluid which may reach the axial passage. The bore 74 in turncommunicates with a bore 76 (FIG. 4) in the head 32 of pump 10. A plug78 is threadably received in the bore 76 of the head for closing thedrain.

Referring to FIG. 4, first and second annular seals 80, 82 arepositioned in the axial passage 52 generally co-axial with the passageand spaced from one another longitudinally of the passage. The first(upper) seal 80 is positioned in the upper section 62 of the axialpassage adjacent the upper shoulder 68, and the second (lower) seal 82is positioned in the lower section 66 of the passage adjacent the lowershoulder 70. Each seal surrounds the plunger 44 and is sized for sealingcontact therewith. The upper seal 80 is removably retained in the uppersection 62 of the axial passage adjacent the upper shoulder by a packingnut 84 threaded down in the gland 50. The lower seal 82 is removablyretained in the lower section 66 of the axial passage by a retainingring 85 received in an internal groove of the gland. A flat washer 86 isdisposed between the ring 85 and the lower seal 82 to prevent damage tothe seal. In one embodiment, each of the upper and lower seals 80, 82 isa cup seal having a generally U-shaped cross-sectional profile with arectangular base and two opposing legs extending from the base defininga recess between the legs. The opposing legs are asymmetrical andconfigured to remain in sealing contact with respective surfaces of thegland 50 and plunger 44. A tip 88 of the radially inner leg has achamfered edge which comprises a wiping surface in contact with theplunger 44. The seals 80, 82 are oriented with the legs pointed towardthe chamber 42 (downward in FIG. 4) for effective sealing, especiallyduring upstrokes of the plunger 44 when fluid on the surface of theplunger tends to move with the plunger outward from the chamber.

In one embodiment, the first and second seals 80, 82 are substantiallyidentical in size, material, and configuration. However, it isunderstood that the seals can vary without departing from the scope ofthis invention. The seals are made of a suitable material which isstiff, has high mechanical strength, flexibility, and resiliency over arange of pressures. An exemplary material is an elastomer such aspolyurethane having a durometer hardness (Shore A scale) within therange between 87 and 97, and more preferably having a durometer hardnessabout 92. In practice, an effective and commercially available seal is aDisogrin® asymmetrical piston U-cup seal manufactured by Simrit®, havingoffices in Plymouth, Mich.

To reduce friction, particularly resulting from shear forces exerted onthe fluid being pumped, the outer diameter D1 of the plunger 44 is sizedfor a relatively loose clearance fit within the axial passage 52. Inthis regard, the internal diameter D2 of the narrowest section of theaxial passage 52 (the intermediate section 64 of the passage in theillustrated embodiment) is significantly greater than the outer diameterD1 of the plunger 44, defining a clearance or gap G around the plungeras indicated on FIG. 4. In one embodiment, D2 is larger than D1 by atleast about 0.010 inches, and more preferably at least about 0.016inches. This dimensional difference provides a respective average gap Gon each side of the plunger of 0.005 and more preferably 0.008 inches.In practice, that gap is of sufficient width that the shear stress onthe fluid therein is insufficient to produce solidification of UV ink.In one embodiment, D1 is 1.164 inches and D2 is 1.180 inches, providingan average gap G of 0.008 inch on each side of the plunger and adiameter ratio of D2/D1 greater than 1.01.

The relatively loose fit does not produce greater instability or“wobble” in the motion of the plunger 44 because of the sealconfiguration. The two seals 80, 82 function as bearings to guide andstabilize movement of the plunger 44. The spaced-apart positions of theseals in the upper and lower sections 62, 66 of the axial passage,adjacent the narrowest section 64, provide an effective combination forstabilizing the plunger 44. This arrangement avoids the need for asleeve or bearing which would result in increased friction. Further, ifany UV ink fluid does solidify due to friction at the wiping surfaces 88of the first and second seals 80, 82, its adverse effect is minimized bythe relatively short axial length of these wiping surfaces which limitssolidified ink to a narrow line at each wiping surface 88.

Friction is further inhibited by the relatively short longitudinallength of the narrowest section of the axial passage 52, which is theintermediate section 64 in the illustrated embodiment. In oneembodiment, the length L1 of this section is preferably within a rangebetween about 0.4 and 1.0 inches, and more preferably only about 0.9inches. Thus, to the extent any fluid leaks into this area, the shearingforces exerted on fluid are kept to a minimum. In practice, a length L1is about 0.92 inches, providing a ratio of L1 to plunger diameter D1(L1/D1) of about 0.79. That length L1 includes the length of the draingroove 72 which is wider than other portions of the intermediate section64. When the length of the drain groove 72 is subtracted, an effectivelength L1 is about 0.73 inches, providing an effective ratio (L1/D1) ofabout 0.63.

As illustrated in FIG. 5, L1 is less than L2 but greater than L3. By wayof example, L1, L2 and L3 may be 0.92, 1.06, and 0.58 inches,respectively. These dimensions may vary.

In addition, friction is further reduced by the lack of valves orshut-off control in the outlet tube 26 which delivers fluid from theoutlet 40 of the pump chamber to the device 14 requiring fluid. As aresult, the fluid is subjected to only minimal shearing forces and thusless friction, thereby reducing any solidification of the fluid for moreeffective pump operation and longer pump life.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description as shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

1. A reciprocating pump for pumping a fluid, comprising: a pump housinghaving an internal displacement chamber with an inlet, and outlet, alongitudinal axis, and opposite ends; a plunger which is reciprocallymovable in the chamber along said axis; an axial passage in the housingat one end of the chamber through which the plunger axiallyreciprocates; and first and second annular seals in the axial passagegenerally co-axial with the passage and spaced from one anotherlongitudinally of the passage, each seal being sized for sealing contactwith the plunger; wherein the pump housing is free from a bearing whichcontacts the plunger or guides its motion, wherein the plunger is freefrom direct engagement with the housing, and wherein said sealingcontacts of the plunger with the first and second seals are the onlycontacts of the plunger in the housing.
 2. A reciprocating pump as setforth in claim 1 wherein the axial passage comprises an intermediatesection between said seals which is sized to receive the plungertherethrough with a clearance fit.
 3. A reciprocating pump as set forthin claim 2 wherein said intermediate section of the axial passagedefines a minimum clearance region for the plunger in the housing.
 4. Areciprocating pump as set forth in claim 2 wherein the plunger has anouter diameter D1, the intermediate section of the axial passage has aninternal diameter D2, and a ratio of D2 to D1 is greater than 1.01.
 5. Areciprocating pump as set forth in claim 4 wherein D2 is larger than D1by at least about 0.015 inch.
 6. A reciprocating pump as set forth inclaim 2 wherein the plunger has an outer diameter D1, the intermediatesection of the axial passage has an axial length L1, and a ratio of L1to D1 is within a range between 0.5 and 1.0.
 7. A reciprocating pump asset forth in claim 6 wherein said ratio of L1 to D1 is less than 0.8. 8.A reciprocating pump as set forth in claim 2 wherein the intermediatesection of the axial passage has an axial length L1 which is less than1.0 inch.
 9. A reciprocating pump as set forth in claim 2 wherein theaxial passage has internal shoulders at opposite longitudinal ends ofsaid intermediate section, and wherein each of said seals is positionedadjacent a respective shoulder in the axial passage.
 10. A reciprocatingpump as set forth in claim 1 further comprising a threaded nut receivedin the housing, and wherein the axial passage has an internal shouldertherein, one of said seals being retained at a position adjacent saidinternal shoulder by the threaded nut.
 11. A reciprocating pump as setforth in claim 1 wherein each seal has a generally U-shapedcross-section with two opposing legs in respective sealing contact withthe plunger and housing.
 12. A reciprocating pump as set forth in claim11 wherein said two legs of each seal are asymmetrical.
 13. Areciprocating pump as set forth in claim 1 wherein the housing comprisesa pump head, a cylinder attached to the head, and a gland attached tothe head generally opposite the cylinder, and wherein said axial passageis disposed in the gland.
 14. A reciprocating pump as set forth in claim1 wherein the pump is a single-acting pump which, during an upstroke,receives fluid through the inlet into the chamber without simultaneousdischarge through the outlet, and which, during a downstroke, dischargesfluid from the chamber through the outlet.
 15. A reciprocating pump asset forth in claim 1 further comprising drain comprising an annulargroove in the axial passage for draining fluid which is located betweenthe first and second seals.
 16. A reciprocating pump as set forth inclaim 1 in combination with a container for supplying fluid to the inletof the chamber, and a tube for delivering fluid from the outlet of thechamber to a device requiring fluid, and wherein the tube is free fromvalves between the outlet and the device.
 17. A reciprocating pump forpumping a fluid, comprising: a pump housing having an internaldisplacement chamber with an inlet, and outlet, a longitudinal axis, andopposite ends; a plunger which is reciprocally movable in the chamberalong said axis; and an axial passage in the housing at one end of thechamber through which the plunger axially reciprocates, the axialpassage having at least a portion which defines a minimum clearanceregion for the plunger in the housing; wherein the minimum clearanceregion is sized to receive the plunger therethrough with a clearancefit, and wherein the plunger has an outer diameter D1, the minimumclearance region has an internal diameter D2, and wherein D2 is largerthan D1 by at least about 0.015 inch.
 18. A reciprocating pump as setforth in claim 17 wherein a ratio of D2 to D1 is greater than 1.01. 19.A reciprocating pump as set forth in claim 17 further comprising firstand second annular seals positioned in the axial passage generallyco-axial with the passage and spaced from one another longitudinally ofthe passage, each seal being sized for sealing contact with the plunger.20. A reciprocating pump for pumping a fluid, comprising: a pump housinghaving an internal displacement chamber with an inlet, and outlet, alongitudinal axis, and opposite ends; a plunger which is reciprocallymovable in the chamber along said axis; and an axial passage in thehousing at one end of the chamber through which the plunger axiallyreciprocates, the axial passage having at least a portion which definesa minimum clearance region for the plunger in the housing; wherein theminimum clearance region of the axial passage has an axial length L1which is less than 1.0 inch.
 21. A reciprocating pump as set forth inclaim 20 wherein the plunger has a radial diameter D1, and a ratio of L1to D1 is less than 0.8.
 22. A reciprocating pump as set forth in claim20 further comprising first and second annular seals positioned in theaxial passage generally co-axial with the passage and spaced from oneanother longitudinally of the passage, each seal being sized for sealingcontact with the plunger.
 23. A reciprocating pump for pumping a fluid,comprising: a pump housing having an internal displacement chamber withan inlet, and outlet, a longitudinal axis, and opposite ends, thehousing including a pump head, a cylinder attached to the head, and agland attached to the head generally opposite the cylinder; a plungerwhich is reciprocally movable in the chamber along said axis; an axialpassage in the gland through which the plunger axially reciprocates; andfirst and second annular seals in the axial passage generally co-axialwith the passage and spaced from one another longitudinally of thepassage, each seal being sized for sealing contact with the plunger andhaving a generally U-shaped cross-section with two opposing legs inrespective sealing contact with the plunger and housing, wherein saidtwo legs of each seal are asymmetrical; wherein the axial passagecomprises an intermediate section between said seals which is sized toreceive the plunger therethrough with a clearance fit; internalshoulders at opposite longitudinal ends of said intermediate section,each of said seals being positioned adjacent a respective shoulder inthe axial passage, at least one of said seals being retained by athreaded nut; and wherein the pump housing is free from a bearing whichcontacts the plunger or guides its motion, the plunger being free fromdirect engagement with the housing, and wherein said sealing contacts ofthe plunger with the first and second seals are the only contacts of theplunger in the housing.